Single prism aberration compensation

ABSTRACT

System and method for utilizing two prisms spatially separated is provided. The two prisms spatially separated allows the two prisms typically found in a TIR optical relay system to be spatially separated. In an embodiment, one or more optical relay lenses are interposed between the two prisms. The prism positioned on the object side may be integrated into one or more of the optical relay lenses, thereby further simplifying the optical relay design. In another embodiment, the one or more optical relay lenses may have an optical axis that is offset from the optical axis of incoming light to cause a pupil shift. An aspherical lens may be included to correct for the pupil shift and create a more uniform illumination image.

This application is a Divisional of application Ser. No. 11/948,827filed Nov. 30, 2007 (now U.S. Pat. No. 7,742,229).

TECHNICAL FIELD

Embodiments relate generally to the field of projection display systemsand, more particularly, to an optical system utilizing a singlerefractive prism operating in total internal reflection mode.

BACKGROUND

Projection displays are used for a wide variety of applications, such asproducing the pictures viewed on television screens. A typicalprojection display system includes a number of components, including adisplay screen, a light source, and an optical path between them. Tocreate the pictures, one or more light sources are provided to emitlight when it is needed. The light they produce is then manipulated by aseries of optical devices in order to create the visual image. Thevisual image created along the optical path is then displayed on thedisplay screen, the television screen for example, or another visualdisplay. In most cases, the goal is to produce the best picturepossible. The key to producing a desirable visual display, of course, isthe configuration of the various optical devices along the optical path.The selection, operation, and configuration of these devices alsocontribute to unseen characteristics of the system, such as cost andefficient use of system resources.

Several types of projection displays have recently been developed. Thesenew display systems are now becoming much more common, serving as areplacement for the widely-used CRT (cathode ray tube) display, whichproduces a visual image by producing and directing a stream of electronsat a treated display surface. The stream could only be directed to onepoint at any given time, but can be systematically swept across thedisplay with such speed as to create the visual impression of a singleimage. This technology is fairly well-developed, but has reached thepoint where perceptible increases in quality are difficult to achieve. ACRT also takes up a relatively-large amount of space because thecomponents used for generating the electron stream must be placed at acertain distance from the display screen. Many recently-developedprojection display systems, in contrast, feature a much slimmer profile.In addition, projection display systems often produce much cleanervisual images. The combination of these advantages has made such systemsimmensely popular.

One such projection-display system is commercially available from TexasInstruments of Dallas, Tex. under the trademark DLP® (or Digital LightProcessing®). DLP® projection-display systems utilize a digitalmicromirror device (DMD) in their optical path. The DMD typicallyincludes an array of thousands of tiny mirrors that are used tomanipulate light originating at an internal light source. Lenses andother components in the optical path adjust the light for use by theDMD, or convey the image it generates to a display plane.

Most such systems utilize a total internal reflection (TIR) prismarrangement or reverse TIR(RTIR) prism arrangement. With TIR prismarrangements wherein light is internally reflected on the image side,light modulated from the DMD intersects two complementary prismsequivalent to a parallel plate. With RTIR arrangements wherein the lightis internally reflected on the projection side, the prisms must be suchthat lateral color and geometrical aberrations introduced by both prismsare partially compensating each other. In both of these types ofsystems, two prisms are used to compensate for aberrations, such aslateral color, anamorphic magnification, astigmatism, and the like, thatusing a single prism may cause.

The use of TIR or RTIR arrangements, however, requires extremelyconstraining manufacturing tolerances and is expensive to fabricate andto assemble. In particular, the prisms of TIR or RTIR arrangements aregenerally aligned such that the surfaces of the prisms are parallel andextremely close. Furthermore, the TIR or RTIR arrangements may exhibitcontrast problems due to the high angle of incidence on both surfacescreating the gap between the two prisms inducing multiple parasiticreflections close to the focal plane and therefore degrading thecontrast.

SUMMARY OF THE INVENTION

These and other problems are generally solved or circumvented, andtechnical advantages are generally achieved, by embodiments of thepresent invention which provide a system and a method for utilizing asingle TIR prism to compensate for aberrations.

In accordance with an embodiment, an optical system is provided. Theoptical system includes a light source, a receiving plane, and a firstlens system interposed between the light source and the receiving planefor directing light from the light source to the receiving plane. Thefirst lens system includes a first optical element, a first prism, andone or more relay lenses interposed between the first optical elementand the first prism. The first optical element causes a prismatic effectand may comprise a prism concatenated to a lens. The first opticalelement may have a spherical surface, an aspherical surface, or a flatsurface. The first optical element may also comprise a Fresnel lens or alens having an optical power. The optical axes of the one or more relaylenses may be offset from the optical axis of incoming light.Furthermore, one or more of the optical relay lenses may have aspherical surface, an aspherical surface, or a flat surface.

In accordance with another embodiment, a method of providing light to areceiving plane is provided. Light is provided along a first axis to afirst optical element, which is tilted relative to the first axis. Lightleaving the first optical element is provided to one or more relaylenses, which provides the light to a first prism. Light leaving thefirst prism is directed to the receiving plane, such as a spatial lightmodulator. The first optical element causes a prismatic effect and maybe a concatenation of a prism and a lens, such as a lens having aspherical surface or an aspherical surface. The first optical elementmay also comprise a Fresnel or powered lens. The optical axes of the oneor more relay lenses may be offset from the optical axis of incominglight. Furthermore, one or more of the optical relay lenses may have anaspherical surface.

In accordance with yet another embodiment, an optical arrangement isprovided. The optical arrangement includes a TIR assembly, whichincludes a first prism and a second prism. The first prism and thesecond prism of the TIR assembly are spatially separated and one or moreintermediate lenses are interposed between the first prism and thesecond prism along an optical path. The one or more intermediate lensespreferably have an optical axis that is parallel to the optical axis ofthe incoming light. The optical axis of the one or more intermediatelenses, however, may be offset from the optical axis of the incominglight or tilted or both. The first prism of the TIR assembly maycomprise a first prism combined with another lens, such as a sphericallens, aspherical lens, a Fresnel lens, a lens having an optical power,or the like, combined into a single lens. One or more of theintermediate lenses may also include an aspherical lens to correct forspherical aberration when the lens is shifted, for example, to introducea pupil shift and for pupil aberration as well or distortion correction.

The foregoing has outlined rather broadly the features and technicaladvantages of some of the embodiments of the present invention in orderthat the detailed description of the invention that follows may bebetter understood. Additional features and advantages of the inventionwill be described hereinafter which form the subject of the claims ofthe invention. It should be appreciated by those skilled in the art thatthe conception and specific embodiments disclosed may be readilyutilized as a basis for modifying or designing other structures orprocesses for carrying out the same purposes of the present invention.It should also be realized by those skilled in the art that suchequivalent constructions do not depart from the spirit and scope of theinvention as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantagesthereof, reference is now made to the following descriptions taken inconjunction with the accompanying drawings, in which:

FIG. 1 is a diagram of different views of an exemplary DMD-basedprojection display system;

FIG. 2 illustrates an optical system that may be used in accordance withan embodiment;

FIG. 3 illustrates an optical system that may be used in accordance withanother embodiment; and

FIG. 4 illustrates another optical system that may be used in accordancewith yet another embodiment.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments are discussed in detail below.It should be appreciated, however, that the present invention providesmany applicable inventive concepts that can be embodied in a widevariety of specific contexts. The specific embodiments discussed aremerely illustrative of specific ways to make and use the invention, anddo not limit the scope of the invention.

The embodiments will be described in a specific context, namely aDMD-based projection display system. Embodiments may also be applied,however, to projection display systems in general. Furthermore, whileembodiments will be described with reference to DMDs, other spatiallight modulators (SLMs) may be used.

Additionally, embodiments of the present invention may be utilized inother types of systems besides projection display systems. Inparticular, other embodiments may be utilized in other types of systemswherein using a prism may be desirable to obtain wavelength dispersionand deviation without the associated aberrations, such as lateral coloraberrations, anamorphic magnification aberrations, astigmatism, or thelike. For example, systems in which embodiments may be utilized inspectrometers, imaging applications, or the like. In the example of aspectrometer, light is intentionally dispersed through a prismaticelement and optical quality is required with a source with low extensionin one direction (slit) but with high angular dispersion to provideoptimum spectral resolution. In other imaging applications, such asHyperSpectral applications, the source can be extended in bothdirections. Projection display systems are used herein simply toillustrate an embodiment as an example.

With reference now to FIG. 1 is a diagram illustrating views of anexemplary DMD-based projection display system. The diagram shown in FIG.1 illustrates a high-level view of a DMD-based projection display system100, which includes a DMD 105 that modulates light produced by a lightsource 110. The DMD 105 is an example of a microdisplay. In amicrodisplay, an array of light modulators may be arranged in arectangular, square, diamond shaped, and so forth, array. Each lightmodulator in the microdisplay may operate in conjunction with the otherlight modulators to modulate the light produced by the light source 110.The light, modulated by the DMD 105, may be used to create images on adisplay plane 115. The DMD-based projection display system 100 alsoincludes a first optical system 120, which may be used to collimate thelight produced by the light source 110 as well as collect stray light,and a second optical system 125, which may be used to manipulate (forexample, focus and magnify) the light reflecting off the DMD 105.

The DMD 105 may be coupled to a controller 130, which may be responsiblefor loading image data into the DMD 105, controlling the operation ofthe DMD 105, controlling the light produced by the light source 110, andso forth. A memory 135, which may be coupled to the DMD 105 and thecontroller 130, may be used to store the image data, as well asconfiguration data, color correction data, and so forth.

FIG. 2 illustrates an optical path 200 that may be used in the firstoptical system 120 in accordance with an embodiment. In this embodiment,the first optical system 120 includes a first prism P1, a set of relaylenses, denoted generally as reference numeral 210, and a second prismP2. In operation, the optical path 200 includes light deviated through afirst prism P1 from a light/image source (not shown), such as the lightsource 110 illustrated in FIG. 1. The light passing through the firstprism P1 is reimaged through the set of relay lenses 210. In theembodiment illustrated in FIG. 2, the set of relay lenses 210 includes afirst relay lens L1, a second relay lens L2, and a third relay lens L3,which together shape the polychromatic light beam for the second prismP2.

Light deviated through the second prism P2 is directed to a receivingplane, such as the DMD 105, which modulates the light in accordance witha desired image as described above. The DMD 105 reflects light frompixels in the “on” state back to the second prism P2 such that the lightrays strike the exiting surface P2 _(I) of the second prism P2 at anangle greater than the critical angle. In this manner, the light frompixels in the “on” state is reflected toward the second optical system125 and the display plane 115 (see FIG. 1), as indicated by line 212 inFIG. 2. Light from pixels in the “off” state, on the other hand, isreflected back to the second prism P2 such that the light rays strikethe exiting surface P2 _(O) of the second prism P2 at an angle less thanthe critical angle, thereby allowing the light rays to pass through thesecond prism P2 toward a light sink (not shown), as illustrated by line214 in FIG. 2.

One of ordinary skill in the art will appreciate that the first opticalsystem 120 utilizes a single prism on the image side, e.g., the secondprism P2 in this embodiment, as opposed to two prisms utilized in othertypes of systems utilizing a TIR or RTIR arrangement as discussed above.Embodiments such as that illustrated in FIG. 2 replace a second prismthat is typically placed in close proximity to the second prism P2 withthe first prism P1 on the object side of the relay lenses 210. The firstprism P1 is rotated, flipped, and placed on the object side of the firstset of relay lenses 210 from a position typically used in other systems.In this manner, the placement and alignment of the first prism P1, thefirst set of relay lenses 210, and the second prism P2 relative to eachother is not as critical or as expensive to manufacture as other priorart systems, including the critical alignment of the two prisms relativeto each other. Furthermore, because the first prism P1 is further apartfrom the second prism P2, multiple bounces between both surfacesdefining the gap does not reduce the contrast in the image plane (DMD orother).

It should be noted that, in embodiments such as that illustrated in FIG.2 in which the DMD 105 is used as the SLM, an optical axis 216 of theincoming light is aligned such that the optical axis 216 is notorthogonal to the surface of the DMD 105, as illustrated in FIG. 2 bythe angle DMD_(Tilt). For example, in an embodiment in which the mirrorsrotate +/−12° between the on and off states, the plane orthogonal to theoptical axis 216 is preferably offset about 12° from the surface of theDMD 105. This alignment of the optical axis 216 helps ensure a higherangle of incidence of about 24° on the DMD 105. It should be noted thatthis angle vary depending on the pupil offset (lateral shift of thefirst group and second group of lenses) and the angular deviation powerin the second prism P2.

As illustrated in FIG. 2, the optical axes of the first relay lens L1,the second relay lens L2, and the third relay lens L3, indicated byreference numerals 220, 222, and 224, respectively, may be coincidentwith the optical axis 216 of the first lens system 120. The first prismP1, however, is preferably tilted relative to the optical axis 216 ofthe light/image source such that the surface on the object side of thefirst prism P1, indicated as P1 _(O) in FIG. 2, is not orthogonal to theoptical axis 216, as indicated in as P1 _(Tilt). In an embodiment, P1_(Tilt) is about 33°. Other embodiments, however, may utilize differenttilt angles.

Solely for purposes of illustration, an embodiment may be implementedsuch that the first relay lens L1, the second relay lens L2, and thethird relay lens L3 exhibit the properties as specified in Table I,wherein the subscript “O” refers to the object side and the subscript“I” refers to the image side of each respective optical element.

TABLE I Radius Thickness CAO Tilt Decenter Surface (mm) (mm) (mm) Index(degrees) (mm) Remarks Object Infinity 6 4.5 × 6.0 Air 0 0 Light pipeoutput P1_(O) Infinity 6 12 788475 33 0 P1_(I) Infinity 4 13 air −12 6L1_(O) 801.257 4 9.7 2022291  Lens 1 L1_(I) −24.628 21 10.2 air 0 6Aperture Infinity 16.257 13 air 0 6 Aperture Stop Stop L2_(O) 100.712 1020.7 846238 0 6 L2_(I) −39.894 1 20.9 air 0 6 L3_(O) 35.232 7 16.6805254 0 6 L3_(I) 201.13 11 15 air 6 P2_(O) Infinity 5 17.46 60756633.64 6 Right Angle prism P2_(I) Infinity 6 17.46 air −11.358 6 ImageInfinity 17.46 mirror −11.358 6 DMD Plane

In this embodiment, the second prism P2 is a right-angle prism and ispositioned such that one leg of the right-angle prism is parallel to theDMD 105 and the incoming light from the light source enters the secondprism P2 along the hypotenuse. Preferably, the second prism P2 ispositioned such that the light modulated from the DMD 105 is folded atabout 90 degrees towards projection lens. For that purpose, the angleshould be higher than the critical angle on the hypotenuse of the secondprism P2.

FIG. 3 illustrates another embodiment of the first lens system 120. Inthis embodiment, the first lens system 120 includes an optical elementC1, a fourth relay lens L4, an aspherized lens A1, and a third prism P3.The optical element C1 is substantially equivalent to the concatenationof the first prism P1 and the first relay lens L1 as illustrated in FIG.2. The concatenation of the first prism P1 and the first relay lens L1simplifies the fabrication process, thereby further lowering costs.Furthermore, in some embodiments the optical element C1 may befabricated as a wedge lens, which is a portion of a spherical lens.Spherical lenses, and wedge lenses, may be fabricated relatively easilyand inexpensively, thereby further allowing costs to be reduced.

The fourth relay lens L4 is preferably has an object surface L4 _(O)having a convex surface and an image surface L4 _(I) having a concavesurface. The aspherized lens A1 has a spherical surface A1 _(O) on theobject side and an aspherized surface A1 _(I) on the image side. Theaspherized surface A1 _(I) of the aspherized lens A1 helps correct forpupil non-uniformity. It has been found that the tilting and decenteringof the optical element C1 and/or the use of the aspherized lens A1 helpsoptimize the DMD illumination uniformity (near field and far field).

In a preferred embodiment, optical axes of the fourth relay lens L4 andthe aspherized lens A1 are not coincident with the optical axis 216 ofthe incoming light. Rather, in a preferred embodiment, the fourth relaylens L4 preferably has an optical axis 312 and the aspherical lens A1has an optical axis 314 that is parallel to the optical axis 216 of theincoming light, but is not coincident with the optical axis 216 asillustrated in FIG. 3. The optical axis 312 of the fourth relay lens L4and the optical axis 314 of the aspherical lens A1 are parallel to, butoffset from, the optical axis 216. In this manner, the fourth relay lensL4 causes an optical pupil shift while the aspherized lens A1 with theaspherized surface A1 _(I) corrects for the pupil illuminationuniformity.

In a preferred embodiment, the optical element C1 has a surface on theobject side, indicated by reference numeral C1 _(O), is tilted from aplane orthogonal to the optical axis 216. This tilt is indicated in FIG.2 as C1 _(Tilt). Similarly, the surface of the receiving plane, the DMD105 in the embodiment illustrated in FIG. 3, is non-orthogonal tooptical axis 216, as indicated by DMD_(Tilt) in FIG. 3.

Solely for purposes of illustration, an embodiment such as thatillustrated in FIG. 3 may be implemented such that the optical elementC1, the fourth relay lens L4, and the aspherized lens A1 exhibit theproperties as specified in Table II.

TABLE II Radius Thickness CAO Tilt Decenter Surface (mm) (mm) (mm) Index(degrees) (mm) Remarks Object Infinity 8.39 4.5 × 6.0 Air 0 0 Light pipeoutput C1_(O) Infinity 6.533 11 620381 32.61 −1.22 On axis tilted lensC1_(I) 8.3917 24 12 air Aperture Infinity 16 10.2 air 0 Aperture StopStop L4_(O) −120.29 10 21 651585 0 6.64 L4_(I) −31.764 12 22 air A1_(O)30.357 12 18.5 492574 0 3.52 PMMA A1_(I) −32.75 13.44 15 air (cc =−5.11) P2_(O) Infinity 8 18 607566 36.6 Right Angle prism P2_(I)Infinity 6 10.4 air −8.4 Image Infinity 13.34 mirror −8.4 −5 DMD Plane(cc represents the Conic Constant)

It should be noted that the optical element C1 is illustrated having aspherical surface for illustrative purposes only and that otherembodiments may utilize other types of lenses that induces a prismaticeffect. For example, in other embodiments the optical element C1 mayhave a spherical surface, an aspherical surface, a flat surface, or thelike as required by a particular application. As further examples, theoptical element C1 may comprise a wedge, a prism, a spherical lens, anaspherical lens, a Fresnel lens, a lens having an optical power, or thelike in other embodiments.

FIG. 4 illustrates another embodiment of the first lens system 120having two lenses with a tilt and an offset. In this embodiment, thefirst lens system 120 includes an optical element C2, an aspherized lensA2, and a fourth prism P4. Similar to the embodiment discussed abovewith reference to FIGS. 2 and 3, the first prism has been concatenatedwith a lens to form the optical element C2, which simplifies thefabrication process and lowers costs. The optical element C2 maycomprise a lens having a prismatic effect, and may include, for example,a spherical surface, an aspherical surface, or a flat surface. Theoptical element may exhibit properties of a lens, such as a wedge, aprism, a spherical lens, an aspherical lens, a Fresnel lens, a lens withoptical power, or the like in other embodiments.

In an embodiment, the aspherized lens A2 may be substantially similar tothe aspherized lens A1 utilized in the embodiment discussed above withreference to FIG. 3, except that the aspherized lens A1 in thisembodiment is tilted relative to the optical axis 216. Accordingly, inan embodiment, the aspherized lens A2 has a spherical first surface A2_(O) on the object side and an aspherized second surface A2 _(I) on theimage side. The aspherized second surface A2 _(O) of the aspherized lensA2 on the object side helps correct for pupil non-uniformity.

The optical element C2 and the aspherized lens A2 may be tilted relativeto the optical axis 410. In a preferred embodiment, the optical elementC2 is tilted as described above with reference to FIG. 3, and theaspherized lens A2 has an optical axis 414 that is both tilted offsetrelative to the optical axis 216. The positioning of the aspherized lensA2 is further discussed below.

Solely for purposes of illustration, an embodiment such as thatillustrated in FIG. 4 may be implemented such that the optical elementC2, the aspherized lens A2, and the fourth prism P4 exhibit theproperties as specified in Table III.

TABLE III Radius Thickness CAO Tilt Decenter Surface (mm) (mm) (mm)Index (degrees) (mm) Remarks Object Infinity 11.4 4.5 × 6.0 Air 0 0Light pipe output C2_(O) Infinity 6 11.3 822374 20.06 −0.409 C2_(I)Infinity 18.75 11.82 air Aperture 801.257 17 6 air 10.5 0 Aperture StopStop A2_(O) 35.232 12 15.8 585299 23.064 0 Polycarbonate (cc = −3.74)A2_(I) 201.13 13.885 16.4 air (cc = −2.42) P4_(O) Infinity 5 11.9 60756655.57 0 Right Angle prism P4_(I) Infinity 14 10.9 air −10.57 0 ImageInfinity 2.404 12 mirror −10.57 6 DMD Plane (cc represents the ConicConstant)One of ordinary skill in the art will appreciate that the configurationof the embodiments discussed above utilizes a single prism (or otherlens causing a prismatic effect) on the object side (e.g., the lightsource side) and a single prism on the object side (e.g., the receivingplane or DMD side). The configurations discussed above use amagnification of about −1. Other magnifications, however, may beutilized such as magnifications ranging from about −0.8 to about −1.5.Other embodiments may use a smaller or larger magnification, eithernegative or positive sign of magnification.

It should also be understood that other elements may be between theprism on the object side and the light or image source. For example, itmay be desirable to place a lens between the light source and the prismon the object side to magnify the light.

Although the embodiments and their advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, compositionof matter, means, methods and steps described in the specification. Asone of ordinary skill in the art will readily appreciate from thedisclosure of the present invention, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present invention.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

1. An optical system comprising: a light source to produce a light beam,the light source having a first optical axis; a receiving plane; and afirst lens system interposed between the light source and the receivingplane, the first lens system directing the light beam from the lightsource to the receiving plane and including a first optical element, oneor more relay lenses, and a first prism, the one or more relay lensesbeing interposed between the first optical element and the first prism,the first optical element having a prismatic effect.
 2. The opticalsystem of claim 1, wherein the optical element comprises a prismconcatenated with a first lens.
 3. The optical system of claim 1,wherein the optical element has a spherical surface.
 4. The opticalsystem of claim 1, wherein the optical element has an object-sidesurface that is substantially planar, the object-side surface beingtilted with respect to normal to the first optical axis.
 5. The opticalsystem of claim 1, wherein the one or more relay lenses have opticalaxes parallel to and offset from the first optical axis.
 6. The opticalsystem of claim 1, wherein the one or more relay lenses include a firstlens tilted relative to the first optical axis.
 7. The optical system ofclaim 1, wherein the first prism induces an aberration and the opticalelement causes a prismatic effect to substantially correct theaberration.
 8. A method of manufacturing an optical system, the methodcomprising: providing a light source to provide light along a firstaxis; providing a first optical element such that the first opticalelement intercepts light on the first axis, the first optical elementcausing a prismatic effect on the light and having a substantiallyplanar surface facing the light source, the planar surface beingnon-orthogonal to the first axis; providing one or more relay lenses toreceive light from the first optical element; providing a first prism toreceive light from the one or more relay lenses; and providing areceiving plane to receive light from the first prism.
 9. The method ofclaim 8, wherein the first optical element comprises a prismconcatenated with a first lens.
 10. The method of claim 8, wherein theone or more relay lenses have optical axes parallel to and offset fromthe first axis.
 11. The method of claim 8, wherein the one or more relaylenses include a first lens having an aspherical surface.